File size is dictated by bit rate per second, not frames. With a digital camera, the shutter is either open for recording, or shut because it is not.So video quality settings and bit rate is what your dealing with primarily.

Cinemagraphs are still photographs in which a minor and repeated movement occurs, forming a video clip. They are published as an animated GIF or in other video formats, and can give the illusion that the viewer is watching an animation.

Saw something off YouTube that popped up that was related to this video somehow. It's a site called YouTube Doubler. Looks like it allows you to somehow mix two YouTube videos together? Perhaps using the sound track from one for the other?

Not sure how useful it may be, but it looked interesting for messing about.